Radiographic apparatus

ABSTRACT

An object of this invention is to implement a radiographic apparatus which can stably obtain a moving image at a high speed by suppressing a voltage variation in GND or power supply line and omitting the standby period for each frame. To achieve this object, during a period after electrical signals from conversion elements (S 1 - 1 -S 1 - 3 ) in one control interconnection (G 1 ) are transferred and read for each row by a driving circuit section (SR 1 ) before electrical signals in the next control interconnection are transferred and read, the read-accessed conversion elements are refreshed for each row, thereby eliminating the necessity for preparing a refresh period in acquiring continuous moving images. In addition, since the conversion elements are refreshed for each row, the dark current (transient current) in the refresh mode can be made small as compared to a case wherein all the conversion elements are refreshed at once. With this arrangement, the voltage variation in GND or power supply line is suppressed.

This is a divisional application of prior application Ser. No.10/719,123, filed on Nov. 21, 2003, now U.S. Pat. No. 7,042,980, whichis hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a radiographic apparatus which cansuitably be used for medical diagnosis or industrial nondestructiveinspection. In this specification, radiation includes electromagneticwaves such as X-rays and γ-rays, or α-rays and β-rays.

BACKGROUND OF THE INVENTION

Conventional X-ray imaging systems installed in hospitals and the likecan be classified into a film photographing scheme which irradiates apatient with X-rays and exposes the X-rays transmitted through thepatient to a film and an image processing scheme which converts X-raystransmitted through a patient into an electrical signal and executesdigital image processing.

An example of apparatuses using the image processing scheme is aradiographic apparatus comprising a phosphor which converts X-rays intovisible light and a photoelectric conversion device which converts thevisible light into an electrical signal. The phosphor is irradiated withX-rays that have passed through a patient. The internal information ofthe patient, which is converted into visible light by the phosphor, isoutput from the photoelectric conversion device as an electrical signal.When the internal information of the patient is converted into anelectrical signal, the electrical signal can be converted into digitaldata by an A/D converter. In this case, the X-ray image information tobe used for recording, display, printing, and diagnosis can be handledas digital values.

Recently, radiographic apparatuses in which an amorphous siliconsemiconductor thin film is used in a photoelectric conversion devicehave been put into practical use.

FIG. 24 is a plan view of a conventional photoelectric conversionsubstrate formed by using amorphous silicon semiconductor thin films asthe materials of a MIS photoelectric conversion element 101 and switchelement 102. FIG. 24 also shows interconnections that connect theelements.

FIG. 25 is a sectional view taken along a line A-B in FIG. 24. For thesake of simplicity, the MIS photoelectric conversion element will simplybe referred to as a photoelectric conversion element hereinafter.

As shown in FIG. 25, the photoelectric conversion element 101 and switchelement 102 (amorphous silicon TFT; to simply be referred to as a TFThereinafter) are formed on a single substrate 103. The lower electrodeof the photoelectric conversion element 101 is formed from a first metalthin-film layer 104 that is the same as the layer that forms the lowerelectrode (gate electrode) of the TFT 102. The upper electrode of thephotoelectric conversion element 101 is formed from a second metalthin-film layer 105 that is the same as the layer that forms the upperelectrode (source and drain electrodes) of the TFT 102.

The first and second metal thin-film layers 104 and 105 are also sharedby a gate driving interconnection 106 and matrix signal interconnection107 in the photoelectric conversion circuit section shown in FIG. 24.FIG. 24 shows 2×2=4 pixels. The hatched portions in FIG. 24 indicate thelight-receiving surfaces of the photoelectric conversion elements 101. Apower supply line 109 supplies a bias to the photoelectric conversionelement 101. A contact hole 110 connects the photoelectric conversionelement 101 to the TFT 102.

When the structure shown in FIG. 24, which mainly uses an amorphoussilicon semiconductor, is used, the photoelectric conversion element101, TFT 102, gate driving interconnection 106, and matrix signalinterconnection 107 can be simultaneously formed on a single substrate.The photoelectric conversion circuit section having a large area caneasily be provided at a low cost.

The device operation of the photoelectric conversion element 101 will bedescribed next with reference to FIG. 26. In FIG. 26, a to c show agraph showing energy bands so as to explain the device operation of thephotoelectric conversion element 101 shown in FIGS. 24 and 25.

In FIG. 26, a and b show the operations in a refresh mode and in aphotoelectric conversion mode, respectively. The abscissa indicates thestates of the respective layers shown in FIG. 25 in the direction offilm thickness. M1 indicates a lower electrode (G electrode) formed fromthe first metal thin-film layer 104 of, e.g., Cr. An amorphous siliconnitride (a-SiNx) insulating thin-film layer 111 is an insulating layerthat inhibits the passage of both electrons and holes. The amorphoussilicon nitride insulating thin-film layer 111 must be so thick as notto generate a tunneling effect. Genarally, the thickness is 50 nm ormore.

A hydrogenated amorphous silicon (a-Si:H) thin-film layer 112 is aphotoelectric conversion semiconductor layer formed from an intrinsicsemiconductor layer (i-layer) for which doping is intentionallyunexecuted. An N+ layer 113 is an injection inhibiting layer whichinhibits injection of carriers of single conductivity type. The N+ layer113 is made of an amorphous semiconductor such as an n-type hydrogenatedamorphous silicon thin-film layer that is formed to prevent holeinjection to the hydrogenated amorphous silicon thin-film layer 112. M2indicates an upper electrode (D electrode) formed from the second metalthin-film layer 105 of, e.g., Al.

Referring to FIG. 25, the D electrode serving as an upper electrode doesnot completely cover the N+ layer 113. However, since electrons canfreely move between the D electrode and the N+ layer 113, the Delectrode and N+ layer 113 always have an equipotential. A descriptionwill be done below on the basis of this condition. The device operationof the photoelectric conversion element 101 includes two operationmodes, i.e., a refresh mode and a photoelectric conversion mode. Thesemodes are based on the manner a voltage is applied to the D electrode orG electrode.

In the refresh mode shown in a of FIG. 26, a negative potential withrespect to the G electrode is applied to the D electrode. Holes in thei-layer 112, which are indicated by filled circles in a of FIG. 26, areguided to the D electrode by the electric field. Simultaneously,electrons indicated by open circles in a of FIG. 26 are injected to thei-layer 112. At this time, some holes and electrons recombine in the N+layer 113 and i-layer 112 and vanish. If this state continues for asufficiently long time, the holes are swept from the i-layer 112.

To change the above-described state to the photoelectric conversion modeshown in b of FIG. 26, a positive potential with respect to the Gelectrode is applied to the D electrode. Accordingly, electrons in thei-layer 112 are instantaneously guided to the D electrode. However,holes are not guided to the i-layer 112 because the N+ layer 113 acts asan injection inhibiting layer. When light becomes incident on thei-layer 112 in this state, the light is absorbed, and electron-holepairs are generated. The electrons are guided to the D electrode by theelectric field. On the other hand, holes move through the i-layer 112and reaches the interface between the i-layer 112 and the amorphoussilicon nitride (a-SiNx) insulating thin-film layer 111. The holescannot move into the insulating layer 111 and therefore stay in thei-layer 112. At this time, the electrons move to the D electrode whilethe holes move to the insulating layer interface in the i-layer. To keepthe electrical neutrality in the photoelectric conversion element 101, acurrent flows from the G electrode. This current corresponds to theelectron-hole pairs generated by light and is therefore proportional tothe incident light.

After the photoelectric conversion mode shown in b of FIG. 26 is heldfor a certain period, the refresh mode shown in a of FIG. 26 is setagain. The holes staying in the i-layer 112 are guided to the Delectrode, as described above. A current corresponding to the holesflows. The number of holes corresponds to the total amount of light thatbecomes incident during the photoelectric conversion mode. At this time,a current corresponding to the number of electrons injected to thei-layer 112 also flows. This number is almost constant and can bedetected by subtraction. That is, the photoelectric conversion element101 can output the amount of light that becomes incident in real timeand also detect the total amount of light that becomes incident during acertain period.

However, if the period of the photoelectric conversion mode becomes toolong due to some reason or the illuminance of incident light is high, nocurrent flows in some cases even when light is incident. This is becausea number of holes stay in the i-layer 112, the electric field in thei-layer 112 becomes small due to these holes, generated electrons arenot guided, and the electrons recombine with the holes in the i-layer112, as shown in c of FIG. 26. This state is called the saturation stateof the photoelectric conversion element 101. When the light incidentstate changes in this state, the current flow may be unstable. However,when the refresh mode is set again, the holes in the i-layer 112 areswept. In the next photoelectric conversion mode, a current proportionalto light flows again.

As described above, if holes in the i-layer 112 should be swept in therefresh mode, all holes are ideally swept. However, an effect can beobtained even by sweeping only some holes. Since a current equal to thatin the above description can be obtained, no problem is posed. That is,only, the necessary thing is to prevent the saturation state shown in cof FIG. 26 in the detection opportunity in the next photoelectricconversion mode. To do this, the potential of the D electrode withrespect to the G electrode in the refresh mode, the period of therefresh mode, and the characteristic of the N+ layer 113 serving as aninjection inhibiting layer are defined.

In the refresh mode, electron injection to the i-layer 112 is not alwaysnecessary. In addition, the potential of the D electrode with respect tothe G electrode is not limited to a negative potential. When a number ofholes are staying in the i-layer 112, the electric field in the i-layer112 is applied to guide the holes to the D electrode even when thepotential of the D electrode with respect to the G electrode ispositive. Furthermore, the N+ layer 113 serving as an injectioninhibiting layer need not always have a characteristic to injectelectrons to the i-layer 112.

FIG. 27 is a circuit diagram showing a conventional photoelectricconversion circuit corresponding to one pixel having the photoelectricconversion element 101 and TFT 102.

Referring to FIG. 27, the photoelectric conversion element 101 includesa capacitance component C_(i) formed from the i-layer and a capacitancecomponent C_(SiN) formed from the injection inhibiting layer. When thephotoelectric conversion element 101 is saturated, i.e., no electricfield (small electric field) is formed between the D electrode and anode N (in the i-layer), the junction (the node N shown in FIG. 27)between the i-layer and the injection inhibiting layer cannot store holecarriers because electrons and holes generated by light recombine.

That is, the potential of the node N is never higher than that of the Delectrode. To embody the operation in this saturation state, a diode(D1) is connected in parallel to the capacitance component C_(i) in FIG.27. That is, the photoelectric conversion element 101 has threeconstituent elements: capacitance component C_(i), capacitance componentC_(SiN), and diode D1.

FIG. 28 is a timing chart showing the operation of the photoelectricconversion circuit corresponding to one pixel shown in FIG. 27. Thecircuit operation of the pixel constituted by the photoelectricconversion element 101 and TFT 102 will be described below withreference to FIGS. 27 and 28.

A refresh operation will be described first.

Referring to FIG. 27, Vs is set to 9 V, and Vref is set to 3 V. In therefresh operation, a switch SW-A is set on the Vref side, a switch SW-Bis set on the Vg(on) side, and a switch SW-C is turned on. In thisstate, the D electrode is biased to Vref (6 V), the G electrode isbiased to the GND potential, and the node N is biased to the maximumVref (6 V). Biasing to the maximum voltage means that if the potentialof the node N is already equal to or higher than Vref in thephotoelectric conversion operation before the current refresh operation,the node N is biased to Vref through the diode D1. If the potential ofthe node N is lower than Vref in the preceding photoelectric conversionoperation, the node N is not biased to the potential Vref by the currentrefresh operation. In actual use, when the photoelectric conversionoperation was repeated a plurality of number of times in the past, thenode N is substantially biased to Vref (6 V) by the current refreshoperation.

After the node N is biased to Vref, the switch SW-A is switched to theVs side. Accordingly, the D electrode is biased to Vs (9 V). With thisrefresh operation, hole carriers stored in the node N of thephotoelectric conversion element 101 are swept to the D electrode side.

An X-ray irradiation period will be described next.

As shown in FIG. 28, a subject is irradiated with X-rays as pulses. Aphosphor Fl is irradiated with the X-rays that have passed through thesubject to be detected so the X-rays are converted into visible light.The semiconductor layer (i-layer) is irradiated with the visible lightfrom the phosphor Fl so the visible light is photoelectricallyconverted. Hole carriers generated by photoelectric conversion arestored in the node N and increase its potential. Since the TFT 102 isOFF, the potential on the G electrode side increases by the same amount.

The wait period is inserted between the refresh period and the X-rayirradiation period. This period is a standby period in which no elementsare operated, and any operation is inhibited until relaxation when thecharacteristic of the photoelectric conversion element 101 is unstabledue to, e.g., a dark current immediately after the refresh operation.When the characteristic of the photoelectric conversion element 101 doesnot become unstable immediately after the refresh operation, the waitperiod need not be prepared.

A transfer operation will be described next.

In the transfer operation, the switch SW-B is set on the Vg(on) side toturn on the TFT 102. Accordingly, electron carriers (Se) correspondingto the number (Sh) of hole carriers stored upon X-ray irradiation flowfrom a C₂ side to the G electrode side through the TFT 102 to increasethe potential of the read capacitor C₂. At this time, Se and Sh holdSe=Sh×C_(SiN)/(C_(SiN)+C_(i)). The potential of the read capacitor C₂ issimultaneously amplified and output through an amplifier. The TFT 102 iskept ON for a time enough to transfer the signal charges and then turnedoff.

A reset operation will be described finally.

In the reset operation, the switch SW-C is turned on, and the readcapacitor C₂ is reset to the GND potential to prepare for the nexttransfer operation.

FIG. 29 is a two-dimensional circuit diagram of the conventionalphotoelectric conversion device.

For the descriptive convenience, FIG. 29 illustrates only 3×3=9 pixels.Reference symbols S1-1 to S3-3 denote photoelectric conversion elements;T1-1 to T3-3, switch elements (TFTs); G1 to G3, gate interconnections toturn on/off the TFTs (T1-1 to T3-3); and M1 to M3, signalinterconnections. A Vs line is an interconnection to apply a storagebias or refresh bias to the photoelectric conversion elements S1-1 toS3-3.

The electrode on the solid side of each of the photoelectric conversionelements S1-1 to S3-3 is a G electrode. A D electrode is formed on theopposite side. The D electrodes share part of the Vs line. To sendlight, a thin N+ layer is used as the D electrodes. The entire structureincluding the photoelectric conversion elements S1-1 to S3-3, TFTs (T1-1to T3-3), gate interconnections G1 to G3, signal interconnections M1 toM3, and Vs line is called a photoelectric conversion circuit section100.

The Vs line is biased by a power supply Vs or power supply Vref. Thepower supplies are switched by a control signal VSC. A shift registerSR1 applies a driving pulse voltage to the gate interconnections G1 toG3. The voltage that turns on the TFTs (T1-1 to T3-3) is externallysupplied. The voltage to be supplied is defined by the power supplyVg(on).

A read circuit section 200 amplifies the parallel signal outputs fromthe signal interconnections M1 to M3 in the photoelectric conversioncircuit section 100, converts the parallel signals into serial signals,and outputs them.

Reference symbols RES1 to RES3 are switches which reset the signalinterconnections M1 to M3; A1 to A3, amplifiers which amplify thesignals from the signal interconnections M1 to M3; CL1 to CL3,sample-and-hold capacitors which temporarily store the signals amplifiedby the amplifiers A1 to A3; Sn1 to Sn3, switches to executesample-and-hold operations; B1 to B3, buffer amplifiers; Sr1 to Sr3,switches to convert the parallel signals into serial signals; SR2, ashift register which supplies a pulse for serial conversion to theswitches Sr1 to Sr3; and Ab, a buffer amplifier which outputs theserially converted signals.

FIG. 30 is a timing chart showing the operation of the photoelectricconversion device shown in FIG. 29. The operation of the photoelectricconversion device shown in FIG. 29 will be described below withreference to this timing chart.

A control signal VSC applies biases of two types to the Vs line, i.e.,the D electrodes of the photoelectric conversion elements S1-1 to S3-3.When the control signal VSC is “Hi”, the D electrode is set to Vref(V).When the control signal VSC is “Lo”, the D electrode is set to Vs(V).The read power supply Vs(V) and refresh power supply Vref(V) are DCpower supplies.

The operation during the refresh period will be described first.

All signals in the shift register SR1 are set to “Hi”, and the CRESsignal in the read circuit section 200 is set to “Hi”. Accordingly, allthe TFTs (T1-1 to T3-3) for switching are turned on. In addition, theswitch elements RES1 to RES3 in the read circuit section 200 are alsoturned on. The G electrodes of all the photoelectric conversion elementsS1-1 to S3-3 are set to the GND potential. When the control signal VSCchanges to “Hi”, the D electrodes of all the photoelectric conversionelements S1-1 to S3-3 are biased to the refresh power supply Vref(negative potential). All the photoelectric conversion elements S1-1 toS3-3 are set in the refresh mode, and refresh is performed.

A photoelectric conversion period will be described next.

When the control signal VSC switches to “Lo”, the D electrodes of allthe photoelectric conversion elements S1-1 to S3-3 are biased to theread power supply Vs (positive potential). The photoelectric conversionelements S1-1 to S3-3 are set in the photoelectric conversion mode. Inthis state, all the signals in the shift register SR1 are set to “Lo”,and the CRES signal in the read circuit section 200 is set to “Lo”.Accordingly, all the TFTs (T1-1 to T3-3) for switching are turned off.In addition, the switch elements RES1 to RES3 in the read circuitsection 200 are also turned off. The G electrodes of all thephotoelectric conversion elements S1-1 to S3-3 are set in a DC openstate. However, the potential is held because the photoelectricconversion elements S1-1 to S3-3 also have capacitance components asconstituent elements.

At this time, since no light is incident on the photoelectric conversionelements S1-1 to S3-3, no charges are generated. That is, no currentflows. When the light source is turned on to emit a pulse, the Delectrodes (N+ electrodes) of the photoelectric conversion elements S1-1to S3-3 are irradiated with light, and a so-called photocurrent flows.The light source is not particularly illustrated in FIG. 29. For, e.g.,a copying machine, a fluorescent lamp, LED, or halogen lamp is used. Foran X-ray imaging apparatus, an X-ray source is used literally. In thiscase, a scintillator that converts X-rays into visible light is used.The photocurrent generated by the light is stored in the photoelectricconversion elements S1-1 to S3-3 as charges. The charges are held evenafter the light source is turned off.

A read period will be described next.

A read operation is performed in the order of the photoelectricconversion elements S1-1 to S1-3 of the first row, the photoelectricconversion elements S2-1 to S2-3 of the second row, and thephotoelectric conversion elements S3-1 to S3-3 of the third row.

First, to read the photoelectric conversion elements S1-1 to S1-3 of thefirst row, a gate pulse is applied from the shift register SR1 to thegate interconnection G1 of the switch elements (TFTs) T1-1 to T1-3. Atthis time, the high level of the gate pulse equals the externallysupplied voltage V(on). Accordingly, the TFTs (T1-1 to T1-3) are turnedon. Signal charges stored in the photoelectric conversion elements S1-1to S1-3 are transferred to the signal interconnections M1 to M3.

Although not particularly illustrated in FIG. 29, a read capacitor isadded to each of the signal interconnections M1 to M3. The signalcharges are transferred to the read capacitors through the TFTs (T1-1 toT1-3). For example, the read capacitor added to the signalinterconnection M1 corresponds to the sum of (three) interelectrodecapacitances (Cgs) between the gates and sources of the TFTs (T1-1 toT3-1) connected to the signal interconnection M1. The signal chargestransferred to the signal interconnections M1 to M3 are amplified by theamplifiers A1 to A3. The capacitor corresponds to C₂ shown in FIG. 27.When the CRES signal is turned on, the signal charges are transferred tothe sample-and-hold capacitors CL1 to CL3 and held when the CRES signalis turned off.

When a pulse is applied from the shift register SR2 to the switches Sr1,Sr2, and Sr3 in this order, the signals held by the sample-and-holdcapacitors CL1 to CL3 are output from the buffer amplifier Ab in theorder of the sample-and-hold capacitors CL1, CL2, and CL3. As a result,photoelectric conversion signals of one row including the photoelectricconversion elements S1-1, S1-2, and S1-3 are sequentially output. Theread operation of the photoelectric conversion elements S2-1 to S2-3 ofthe second row and the read operation of the photoelectric conversionelements S3-1 to S3-3 of the third row are executed in the same way asdescribed above.

When the signals of the signal interconnections M1 to M3 are sampled andheld by the sample-and-hold capacitors CL1 to CL3 in accordance with aSMPL signal of the first row, the signal interconnections M1 to M3 canbe reset to the GND potential by the CRES signal. After that, a gatepulse can be applied to the gate interconnection G2. That is, while thesignals of the first row are serially converted by the shift registerSR2, the signal charges in the photoelectric conversion elements S2-1 toS2-3 of the second row can be simultaneously transferred in the shiftregister SR1.

With the above operation, the signal charges of all the photoelectricconversion elements S1-1 to S3-3 of the first to third rows can beoutput.

The above-described operation of the X-ray imaging apparatus is anoperation for acquiring one still image by executing the refreshoperation, irradiating the subject with X-rays, and executing the readoperation. To acquire continuous moving images, the timing chart shownin FIG. 30 is repeatedly executed a number of times corresponding to thedesired number of moving images.

However, to particularly obtain moving images by using an X-ray imagingapparatus with an enormous number of pixels, the frame frequency must befurther increased. If the refresh operation of photoelectric conversionelements is executed through a Vs line common to all the photoelectricconversion elements, one refresh period must be essentially provided inone frame. This decreases the frame frequency, i.e., decreases theoperation speed especially in acquiring moving images.

Generally, specifications necessary for simple imaging of a breast partshould include an imaging area of 40 cm square or more and a pixel pitchof 200 μm or less. If an X-ray imaging apparatus is constructed with animaging area of 40 cm square and a pixel pitch of 200 μm, 4,000,000photoelectric conversion elements are necessary. When such a largenumber of pixels are refreshed at once, the current that flows in therefresh mode becomes large. Since the voltage variation in GND or powersupply line of the X-ray imaging apparatus increases, no stable imagingcan be executed.

For an image of a certain type required, an X-ray irradiation standbytime must be provided until the voltage variation relaxes. Although notillustrated in FIG. 30, the standby time corresponds to the wait periodshown in FIG. 28. That is, to refresh all photoelectric conversiondevices at once, one refresh period is necessary in one frame, andadditionally, one wait period is necessary in one frame.

SUMMARY OF THE INVENTION

The present invention has been made in consideration of theabove-described problems, and has as its object to provide aradiographic apparatus which can stably obtain moving images at a highspeed by suppressing the voltage variation in GND and power supply lineand omitting the standby time in each frame.

In order to solve the above-described problems and achieve the aboveobject, according to the first aspect of the present invention, there isprovided a radiographic apparatus comprising a conversion circuitsection in which pixels each including a conversion element thatconverts incident radiation into an electrical signal and a switchelement that transfers the electrical signal are two-dimensionallyarrayed, and which comprises a control interconnection that connects thepixels in a row direction and a signal interconnection that reads theelectrical signal from the conversion element through the switchelement, a driving circuit section which sequentially drives a pluralityof control interconnections, and a read circuit section which isconnected to a plurality of signal interconnections and reads theelectrical signal from the conversion element for each row, wherein theread circuit section includes a refresh device which refreshes each rowby applying a first bias to the read-accessed conversion element, and areset device which executes reset by applying a second bias to thesignal interconnection by using at least one reset switch.

According to the second aspect of the present invention, there isprovided a radiographic apparatus comprising a conversion circuitsection in which pixels each including a conversion element thatconverts incident radiation into an electrical signal and a first switchelement that transfers the electrical signal are two-dimensionallyarrayed, and which comprises a control interconnection that connects thepixels in a row direction and a signal interconnection that reads theelectrical signal from the conversion element through the first switchelement, a driving circuit section which sequentially drives a pluralityof control interconnections, and a read circuit section which isconnected to a plurality of signal interconnections and reads theelectrical signal from the conversion element for each row, wherein theread circuit section comprises a current integration type operationalamplifier at a first stage, the operational amplifier comprises, betweenan inverting terminal and an output terminal, a capacitive element tointegrate the electrical signal transferred from the conversion elementthrough the first switch element and a second switch element to resetthe capacitive element, and the operational amplifier comprises, at anoninverting terminal, a bias supply device which selectively suppliesat least two biases comprising a first bias and a second bias, a refreshdevice which refreshes each row by applying the first bias to theconversion element read-accessed by using the first switch element andthe second switch element, and a reset device which executes reset byapplying the second bias to the capacitive element by using the secondswitch element.

According to the third aspect of the present invention, there isprovided a radiographic system comprising a radiation source whichirradiates a person or object to be examined with radiation, theabove-described radiographic apparatus, which detects the radiation, animage processing apparatus which converts an electrical signal outputfrom the radiographic apparatus into digital data and executes imageprocessing, and a display apparatus which displays the image processedby the image processing apparatus.

According to the fourth aspect of the present invention, there isprovided a driving method for a radiographic apparatus having aconversion circuit section in which pixels each including a conversionelement that converts incident radiation into an electrical signal and aswitch element that transfers the electrical signal aretwo-dimensionally arrayed, and which comprises a control interconnectionthat connects the pixels in a row direction and a signal interconnectionthat reads the electrical signal from the conversion element through theswitch element, a driving circuit section which sequentially drives aplurality of control interconnections, and a read circuit section whichis connected to a plurality of signal interconnections and reads theelectrical signal from the conversion element for each row, comprising arefresh step of refreshing each row by applying a first bias to theconversion element read-accessed by the read circuit section, and areset step of executing reset by applying a second bias to the signalinterconnection by using at least one reset switch.

The present invention has the above-described technical means. During aperiod after electrical signals from conversion elements in one controlinterconnection are transferred and read for each row by the drivingcircuit section (shift register) before electrical signals in the nextcontrol interconnection are transferred and read, the conversionelements in the read-accessed control interconnection can be refreshedfor each row. For this reason, the necessity for preparing a refreshperiod in acquiring continuous moving images can be eliminated. Withthis arrangement, since the frame frequency in acquiring moving imagescan be increased, moving images can be obtained at a high speed. Inaddition, since the conversion elements are refreshed for each row, thedark current (transient current) in the refresh mode can be made smallas compared to a case wherein all the conversion elements are refreshedat once. With this arrangement, the voltage variation in GND or powersupply line is suppressed, and the wait time necessary for relaxing thevoltage variation can be omitted.

Other features and advantages of the present invention will be apparentfrom the following description taken in conjunction with theaccompanying drawings, in which like reference characters designate thesame or similar parts throughout the figures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an equivalent circuit diagram of one pixel of an X-ray imagingapparatus according to the first embodiment of the present invention;

FIG. 2 is a timing chart showing the circuit operation of one pixel ofthe X-ray imaging apparatus shown in FIG. 1;

FIG. 3 is an equivalent circuit diagram of the X-ray imaging apparatusaccording to the first embodiment;

FIG. 4 is a timing chart showing the operation of the X-ray imagingapparatus shown in FIG. 3;

FIG. 5 is a timing chart showing an operation performed when the X-rayimaging apparatus according to the first embodiment is continuously (ina DC manner) irradiated with X-rays;

FIG. 6 is an equivalent circuit diagram of one pixel of an X-ray imagingapparatus according to the second embodiment of the present invention;

FIG. 7 is an equivalent circuit diagram of the X-ray imaging apparatusaccording to the second embodiment;

FIG. 8 is a timing chart showing an operation performed when afluoroscopy mode (moving image mode) of the X-ray imaging apparatusaccording to the second embodiment is changed to an imaging mode (stillimage mode) to execute imaging;

FIG. 9 is a timing chart of the fluoroscopy mode in FIG. 8;

FIG. 10 is another timing chart of the fluoroscopy mode in FIG. 8;

FIG. 11 is a timing chart of the imaging mode in FIG. 8;

FIG. 12 is an equivalent circuit diagram of one pixel of an X-rayimaging apparatus according to the third embodiment of the presentinvention;

FIG. 13 is a timing chart showing the circuit operation of one pixel ofthe X-ray imaging apparatus shown in FIG. 12;

FIG. 14 is an equivalent circuit diagram of the X-ray imaging apparatusaccording to the third embodiment;

FIG. 15 is a timing chart showing the operation of the X-ray imagingapparatus shown in FIG. 14;

FIG. 16 is a timing chart showing an operation performed when the X-rayimaging apparatus according to the third embodiment is continuously (ina DC manner) irradiated with X-rays;

FIG. 17 is an equivalent circuit diagram of one pixel of an X-rayimaging apparatus according to the fourth embodiment of the presentinvention;

FIG. 18 is an equivalent circuit diagram of the X-ray imaging apparatusaccording to the fourth embodiment;

FIG. 19 is a timing chart showing an operation performed when afluoroscopy mode (moving image mode) of the X-ray imaging apparatusaccording to the fourth embodiment is changed to an imaging mode (stillimage mode) to execute imaging;

FIG. 20 is a timing chart of the fluoroscopy mode in FIG. 19;

FIG. 21 is another timing chart of the fluoroscopy mode in FIG. 19;

FIG. 22 is a timing chart of the imaging mode in FIG. 19;

FIG. 23 is a schematic view showing an application example of theradiographic apparatus according to the present invention to an X-raydiagnostic system;

FIG. 24 is a plan view of a conventional photoelectric conversionsubstrate formed by using amorphous silicon semiconductor thin films asthe materials of a photoelectric conversion element and a switchelement;

FIG. 25 is a sectional view taken along a line A-B in FIG. 24;

FIG. 26 is a graph showing energy bands so as to explain the deviceoperation of the photoelectric conversion element shown in FIGS. 24 and25;

FIG. 27 is a circuit diagram showing a conventional photoelectricconversion circuit corresponding to one pixel having a photoelectricconversion element and a TFT;

FIG. 28 is a timing chart showing the operation of the photoelectricconversion circuit corresponding to one pixel shown in FIG. 27;

FIG. 29 is a two-dimensional circuit diagram of the conventionalphotoelectric conversion device; and

FIG. 30 is a timing chart showing the operation of the photoelectricconversion device shown in FIG. 29.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The embodiments of a radiographic apparatus according to the presentinvention will be described next with reference to the accompanyingdrawings. The embodiments will be described by using, an example, aradiographic apparatus having a substrate on which a photoelectricconversion element array are formed by using amorphous siliconsemiconductor thin films as the semiconductor materials of a MISphotoelectric conversion element and a switch element, like the priorart.

(First Embodiment)

FIG. 1 is an equivalent circuit diagram of one pixel of an X-ray imagingapparatus according to the first embodiment of the present invention.

As shown in FIG. 1, a photoelectric conversion element 101 includes acapacitance component C_(i) formed from an i-layer that is made of,e.g., hydrogenated amorphous silicon and serves as a semiconductorphotoelectric conversion layer, and a capacitance component C_(SiN)formed from an insulating layer (an injection inhibiting layer whichinhibits injection of carriers of both conductivity types) that is madeof, e.g., amorphous silicon nitride. When the photoelectric conversionelement 101 is saturated, i.e., no electric field (small electric field)is formed between the D electrode and a node N (in the i-layer), thejunction (the node N shown in FIG. 1) between the i-layer and theinsulating layer cannot store hole carriers because electrons and holesgenerated by light recombine.

That is, the potential of the node N is never higher than that of the Delectrode. To embody the operation in this saturation state, a diode(D1) is connected in parallel to the capacitance component C_(i) inFIG. 1. That is, the photoelectric conversion element 101 has threeconstituent elements: capacitance component C_(i), capacitance componentC_(SiN), and diode D1.

A TFT 102 is thin film transistor serving as a switch element. A powersupply Vs applies a bias to the D electrode of the photoelectricconversion element 101. A read capacitor C₂ is added to the signalinterconnection.

A phosphor FL for waveform conversion is used to convert an X-raywavelength into a visible range wavelength and arranged in direct orindirect contact with the TFT 102. As the matrix material of thephosphor FL, Gd₂O₂S or Gd₂O₃ is used. For the luminescent center, arare-earth element such as Tb₃₊ or Eu₃₊ is used. A phosphor which usesCsI as the matrix material such as CsI:TI or CsI:Na is also used.

A switch SW-C is a reset switch to reset the read capacitor C₂ (signalinterconnection) to a reset bias V(reset). A switch SW-E is a switch torefresh the photoelectric conversion element (G electrode) to a refreshbias V(refresh). The switches SW-C and SW-E are controlled by an RC1signal and an RC2 signal, respectively. Vg(on) is a power supply to turnon the TFT 102 to transfer signal charges to the read capacitor C₂.Vg(off) is a power supply to turn off the TFT 102. A switch SW-Dswitches between the power supply Vg(on) and the power supply Vg(off).

To refresh the photoelectric conversion element 101, the switch SW-Emust be turned on to supply the refresh bias. Simultaneously, a switchSW-D must be set on the power supply Vg(on) side.

FIG. 2 is a timing chart showing the circuit operation of one pixel ofthe X-ray imaging apparatus shown in FIG. 1.

The circuit operation of one pixel having the photoelectric conversionelement 101 and TFT 102 will be described with reference to FIGS. 1 and2.

An X-ray irradiation period will be described first.

As shown in FIG. 2, a subject is irradiated with X-rays as pulses. Thephosphor FL is irradiated with the X-rays that have passed through thesubject to be detected so the X-rays are converted into visible light.The semiconductor layer (i-layer) is irradiated with the visible lightfrom the phosphor FL so the visible light is photoelectricallyconverted. Hole carriers generated by photoelectric conversion arestored in the interface between the i-layer and the insulating layer(injection inhibiting layer) and increase the potential of the node N.Since the TFT 102 is OFF, the potential on the G electrode sideincreases by the same amount. In the X-ray irradiation period, theswitch SW-D is set on the V(off) side, and the switches SW-C and SW-Eare turned off.

A transfer operation will be described next.

In the transfer operation, the switch SW-D is set on the Vg(on) side toturn on the TFT 102. Accordingly, electron carriers (Se) correspondingto the number (Sh) of hole carriers stored upon X-ray irradiation flowfrom a C₂ side to the G electrode side through the TFT 102 to increasethe potential of the read capacitor C₂. At this time, Se and Sh holdSe=Sh×C_(SiN)/(C_(SiN)+C_(i)).

The potential of the read capacitor C₂ is mainly formed from acapacitance including the interelectrode capacitances of all the TFTs102 connected to the signal interconnection. The capacitance is muchlarger than that of the photoelectric conversion element 101. Hence, thepotential increase amount (ΔVC₂) of the read capacitor C₂ after chargetransfer is much smaller than the potential decrease amount (ΔVG) of theG electrode. More specifically, the potential of the read capacitor C₂after transfer is V(reset)+ΔVC₂. This potential almost equals V(reset).Simultaneously, the potential of the read capacitor C₂ is amplified andoutput through an amplifier. An amplifier (AMP) having the most basicform is illustrated in FIG. 1. The amplifier functions as anamplification circuit. The reset bias V(reset) is not a signal componentand is separately canceled. Only ΔVC₂ as a pure signal component isprocessed as a signal.

A refresh operation will be described next.

The timing chart of FIG. 2 shows the potentials of the D electrode, Gelectrode, and node N when Vs=9 (V), Vg(reset)=2 (V), and V(refresh)=6(V) and the capacitance component C_(i) equals the capacitance componentC_(SiN) in the equivalent circuit diagram shown in FIG. 1.

In the refresh operation, the switch SW-C is turned off by the RC1signal. The switch SW-E is turned on by the RC2 signal. The switch SW-Dis set on the Vg(on) side. Accordingly, the potential of the G electrodeof the photoelectric conversion element 101 rises from the potential(V(reset)+ΔVC₂≈V(reset)=2 (V)) at signal transfer to the refresh biasV(refresh)=6 V. Simultaneously, the potential of the node N also risesbut does not exceed Vs=9 V. When the potential of the node N increases,some of the signal charges (hole carriers) stored in the node N aredischarged to the D electrode side, so the refresh operation of thephotoelectric conversion element 101 is executed.

A reset operation will be described next.

In the reset operation, the switch SW-D is kept on the Vg(on) side. Inthis state, the switch SW-C is turned on by the RC1 signal, and theswitch SW-E is turned off by the RC2 signal. Accordingly, the Gelectrode of the photoelectric conversion element 101 and the signalinterconnection C₂ are reset to the reset bias V(reset). Simultaneously,the potential of the node N attenuates from the potential (9 V in FIG.2) in the refresh operation. The attenuation amount ΔVN is ½ of thepotential difference between V(refresh) and V(reset) when thecapacitance component C_(i) equals the capacitance component C_(SiN). Inthis description, the decrease amount is 2 V. In addition, theattenuation amount ΔVN of the node N decides the amount of hole carriersstored in the next photoelectric conversion operation.

In FIG. 28 that shows the prior art, the wait period is prepared.However, no wait period is prepared in the timing chart shown in FIG. 2.The reason will be described below with reference to FIGS. 3 and 4.

FIG. 3 is an equivalent circuit diagram of the X-ray imaging apparatusaccording to the first embodiment. For the descriptive convenience, FIG.3 illustrates only 3×3=9 pixels which are two-dimensionally arrayed in aphotoelectric conversion circuit section 10.

Referring to FIG. 3, reference symbols S1-1 to S3-3 denote photoelectricconversion elements; T1-1 to T3-3, switch elements (TFTs); G1 to G3,gate interconnections to turn on/off the TFTs (T1-1 to T3-3); and M1 toM3, signal interconnections. A Vs line is an interconnection to apply astorage bias to the photoelectric conversion elements.

The electrode on the solid side of each of the photoelectric conversionelements S1-1 to S3-3 is a G electrode. A D electrode is formed on theopposite side. The D electrodes share part of the Vs line. To sendlight, a thin N+ layer is used as the D electrodes. The entire structureincluding the photoelectric conversion elements S1-1 to S3-3, TFTs (T1-1to T3-3), gate interconnections G1 to G3, signal interconnections M1 toM3, and Vs line is called the photoelectric conversion circuit section10.

The Vs line is biased by a power supply Vs. A shift register SR1 appliesa driving pulse voltage to the gate interconnections G1 to G3. Thevoltage Vg(on) that turns on the TFTs (T1-1 to T3-3) and the voltageVg(off) that turns off the TFTs (T1-1 to T3-3) are externally suppliedto the driving circuit section (shift register SR1).

A read circuit section 20 amplifies the parallel signal outputs from thesignal interconnections M1 to M3 in the photoelectric conversion circuitsection 10, converts the parallel signals into serial signals, andoutputs the serial signals.

Reference symbols RES1 to RES3 are switches which reset the signalinterconnections M1 to M3 to the reset bias V(reset). The reset biasV(reset) is indicated by 0 V (GND) in FIG. 3. Reference symbols A1 to A3denote amplifiers which amplify the signals from the signalinterconnections M1 to M3; CL1 to CL3, sample-and-hold capacitors whichtemporarily store the signals amplified by the amplifiers A1 to A3; Sn1to Sn3, switches to execute sample-and-hold operations; B1 to B3, bufferamplifiers; Sr1 to Sr3, switches to convert the parallel signals intoserial signals; SR2, a shift register which supplies a pulse for serialconversion to the switches Sr1 to Sr3; and Ab, a buffer amplifier whichoutputs the serially converted signals.

Reference symbols RES11 to RES33 are switches to refresh the Gelectrodes of the photoelectric conversion elements 101 to the refreshbias V(refresh) through the TFTs (T1-1 to T3-3). The refresh biasV(refresh) is connected to one side of each of the switches RES11 toRES33.

FIG. 4 is a timing chart showing the operation of the X-ray imagingapparatus shown in FIG. 3. FIG. 4 shows the operation of two frames. Theoperation of the photoelectric conversion device shown in FIG. 3 will bedescribed with reference to this timing chart.

A photoelectric conversion period will be described first.

The D electrodes of all the photoelectric conversion elements S1-1 toS3-3 are biased to the read power supply Vs (positive potential). Allsignals in the shift register SR1 are “Lo”. All the TFTs (T1-1 to T3-3)for switching are OFF. When the light source is turned on in this stateto emit a pulse, the D electrodes (N+ electrodes) of the photoelectricconversion elements S1-1 to S3-3 are irradiated with light. Electron andhole carriers are generated in the i-layers of the photoelectricconversion elements S1-1 to S3-3. The electrons are moved to the Delectrodes by the read power supply Vs. Holes are stored in theinterface between the i-layer and the insulating layer of each of thephotoelectric conversion elements S1-1 to S3-3. The holes are held evenafter the power supply is turned off.

A read period will be described next.

A read operation is performed in the order of the photoelectricconversion elements S1-1 to S1-3 of the first row, the photoelectricconversion elements S2-1 to S2-3 of the second row, and thephotoelectric conversion elements S3-1 to S3-3 of the third row.

First, to read the photoelectric conversion elements S1-1 to S1-3 of thefirst row, a gate pulse is applied from the shift register SR1 to thegate interconnection G1 of the switch elements (TFTs) T1-1 to T1-3. Atthis time, the high level of the gate pulse equals the externallysupplied voltage Vg(on). Accordingly, the TFTs (T1-1 to T1-3) are turnedon. Signal charges stored in the photoelectric conversion elements S1-1to S1-3 are transferred to the signal interconnections M1 to M3.

Although not particularly illustrated in FIG. 3, a read capacitor isadded to each of the signal interconnections M1 to M3. The signalcharges are transferred to the read capacitors through the TFTs (T1-1 toT1-3). For example, the read capacitor added to the signalinterconnection M1 corresponds to the sum of (three) interelectrodecapacitances (Cgs) between the gates and sources of the TFTs (T1-1 toT3-1) connected to the signal interconnection M1. The capacitorcorresponds to C₂ shown in FIG. 1. The signal charges transferred to thesignal interconnections M1 to M3 are amplified by the operationalamplifiers A1 to A3. When the SMPL signal is turned on, the signalcharges are transferred to the sample-and-hold capacitors CL1 to CL3 andheld when the SMPL signal is turned off.

When the signals of the signal interconnections M1 to M3 are sampled andheld by the sample-and-hold capacitors CL1 to CL3 in accordance with theSMPL signal of the first row, the signals of the photoelectricconversion elements S1-1 to S1-3 are output from the photoelectricconversion circuit section 10. Hence, the refresh operation of thephotoelectric conversion elements S1-1 to S1-3 in the photoelectricconversion circuit section 10 and the reset operation of the signalinterconnections M1 to M3 can be executed while the signals are beingserially converted by the switches Sr1 to Sr3 in the read circuitsection 20.

In the refresh operation of the photoelectric conversion elements S1-1to S1-3, the switches RES11 to RES33 are turned on by the RC2 signal toapply the voltage Vg(on) to the gate interconnections of the TFTs (T1-1to T3-1). With this operation, the G electrodes of the photoelectricconversion elements S1-1 to S1-3 are refreshed to the refresh biasV(refresh). Then, the reset operation starts.

Subsequently, in the reset operation, while the voltage Vg(on) isapplied to the gate interconnections of the TFTs (T1-1 to T3-1), theswitches RES11 to RES33 are turned off, and the switches RES1 to RES3are turned on. In this way, the read capacitors of the signalinterconnections M1 to M3 and the G electrodes of the photoelectricconversion elements S1-1 to S1-3 are reset to the reset bias V(reset),and in this case, the GND potential.

After the end of the reset operation, a gate pulse can be applied to thegate interconnection G2. More specifically, the signals of the first roware serially converted by the shift register SR2. During this time, inthe photoelectric conversion circuit section 10, the photoelectricconversion elements S1-1 to S1-3 are simultaneously refreshed, and thesignal interconnections M1 to M3 are reset so that the signal charges ofthe photoelectric conversion elements S2-1 to S2-3 of the second row canbe transferred to the signal interconnections M1 to M3 through the shiftregister SR1. With the above operation, the signal charges of all thephotoelectric conversion elements S1-1 to S3-3 of the first to thirdrows can be output.

When the above-described photoelectric conversion period and read periodare repeated, continuous moving images can be acquired.

The timing chart of this embodiment is different from the timing chartof the prior art shown in FIG. 30 in that the refresh period is notpresent in this embodiment. When the refresh period is omitted, theframe frequency in acquiring moving images can accordingly be increased.In the prior art, all the photoelectric conversion elements arerefreshed at once. Hence, the wait period to relax the variation in GNDor power supply due to the dark current component in the refresh modemust be prepared. In this embodiment, however, the photoelectricconversion elements are refreshed for each row. Since the number ofphotoelectric conversion elements to be refreshed at once is muchsmaller than in the prior art, no particular wait period is necessary.Accordingly, the frame frequency can be increased.

In the above-described X-ray imaging apparatus according to thisembodiment, the subject is irradiated with X-rays as pulses. However,X-ray irradiation may be done continuously (in a DC manner). This casewill be described below.

FIG. 5 is a timing chart showing an operation performed when the X-rayimaging apparatus according to the first embodiment is continuously (ina DC manner) irradiated with X-rays.

In this case, the photoelectric conversion period is a period after theend of refresh until the start of transfer. In an actual medical X-rayimaging apparatus, the photoelectric conversion circuit section isconstituted by a number of pixels of N rows×M columns. For example, forthe photoelectric conversion elements of the first row, the actualphotoelectric conversion period equals the read period of the (N−1) rowsfrom the second to Nth rows except the transfer, refresh, and resetperiods of the photoelectric conversion elements. This also applies tothe photoelectric conversion elements of the remaining rows. For them,the actual photoelectric conversion period equals the read period of the(N−1) rows except the transfer, refresh, and reset periods of thephotoelectric conversion elements.

For example, for the photoelectric conversion elements of the 100th row,the actual photoelectric conversion period equals the sum of the readperiod from the 101st to Nth rows and the read period from the first to99th rows in the next frame, i.e., the read period of the (N−1) rows.That is, if a subject is irradiated with X-rays in a DC manner, thephotoelectric conversion period extends over two frames. However, sincethe photoelectric conversion period is the same, no special problem isposed.

When a subject is continuously (in a DC manner) irradiated with X-rays,the X-ray irradiation period shown in FIG. 2 or the photoelectricconversion period shown in FIG. 4 can be omitted. For this reason, theframe rate of moving images can be further increased. In addition, ascompared to the pulse irradiation method, the intensity of X-rays can bereduced. Hence, the load on the tube serving as the X-ray source can bedecreased. Furthermore, since the X-ray high-voltage power supply neednot be pulse-controlled, the load on the X-ray power supply can bereduced.

(Second Embodiment)

FIG. 6 is an equivalent circuit diagram of one pixel of an X-ray imagingapparatus according to the second embodiment of the present invention.In the equivalent circuit diagram of the first embodiment shown in FIG.1, the D electrode of the photoelectric conversion element 101 is biasedby the predetermined voltage Vs. In the second embodiment, however, avoltage Vs and voltage Vref can be switched by a switch SW-F.

As a characteristic feature of this embodiment, the voltage from the Gelectrode side or that from the D electrode side can be selected as anapplication voltage to execute the refresh operation of a photoelectricconversion element 101. For example, to acquire one still image, arefresh bias is applied from the D electrode side. That is, an operationbased on the timing chart shown in FIG. 28 is executed. On the otherhand, to acquire a plurality of still images, a refresh bias is appliedfrom the G electrode side. That is, an operation based on the timingchart shown in FIG. 2 is executed. In this embodiment, both theconventional mode for obtaining a still image (imaging mode or stillimage mode) and the mode for acquiring a moving image (fluoroscopy modeor moving image mode) can be executed by a single X-ray imagingapparatus.

FIG. 7 is an equivalent circuit diagram of the X-ray imaging apparatusaccording to the second embodiment.

The equivalent circuit diagram shown in FIG. 7 is different from FIG. 3in that the bias line of the sensor can be switched between the voltageVs and the voltage Vref by a control signal VSC.

FIG. 8 is a timing chart showing an operation performed when thefluoroscopy mode (moving image mode) of the X-ray imaging apparatusaccording to the second embodiment is changed to the imaging mode (stillimage mode) to execute imaging.

FIG. 9 is a timing chart showing the operation in the fluoroscopy modeof the X-ray imaging apparatus shown in FIG. 7. That is, in thefluoroscopy mode, the timing operation shown in FIG. 8 is repeated.During this period, the radiographer monitors the fluoroscopic image ofthe object (patient) to decide the position or angle of the patient inobtaining a still image. Generally, the intensity of X-ray irradiationduring this period is relatively low. When the radiographer inputs anirradiation request signal (a decision signal for obtaining a stillimage) to the apparatus, the fluoroscopy mode changes to the imagingmode. FIG. 11 shows the operation timing in the imaging mode. In theflow of the fluoroscopy mode and imaging mode, the number of times ofimaging mode is not limited to one, as shown in FIG. 8. The modes may berepeated as fluoroscopy mode→ imaging mode→ fluoroscopy mode→ imagingmode . . . in accordance with the imaging composition of the object.

FIG. 10 is another timing chart in the fluoroscopy mode shown in FIG. 8,which is different from FIG. 9. The difference from FIG. 9 is that thesubject is not irradiated with X-rays as pulses. Since the read andphotoelectric conversion can be executed in the same period, theoperation frequency in the fluoroscopy mode can be increased. Inaddition, since no X-rays as pulses are used, the load on the X-raygeneration source can be reduced.

When the X-ray imaging apparatus of the present invention is applied toa fluoroscopic apparatus, continuous images are acquired in thefluoroscopy mode while executing refresh from the switch side of a readcircuit section 20 through TFTs. When positioning is ended byfluoroscopy, and the fluoroscopy mode is changed to the still imagemode, refresh can be executed from the switch SW-F to obtain a stillimage having a high S/N ratio. That is, generally, the efficiency ishigher and the S/N ratio is also higher in refresh from the switch SW-Fside than in refresh from the TFT side. It is reasonable that inobtaining a fluoroscopic positioning image that allows a relatively lowS/N ratio, refresh from the side of the switch of the read circuitsection 20 is employed. On the other hand, in obtaining a still imagethat requires a high S/N ratio and high image quality, refresh from theswitch SW-F side is employed.

(Third Embodiment)

FIG. 12 is an equivalent circuit diagram of one pixel of an X-rayimaging apparatus according to the third embodiment. The same referencenumerals or symbols as in the X-ray imaging apparatus shown in FIG. 1denote the same component in FIG. 12. Different constituent elementswill mainly be described below.

A switch SW-G shown in FIG. 12 is selectively switched to apply one of areset bias V(reset) and refresh bias V(refresh) to the noninvertingterminal (+) of the operational amplifier (AMP). A capacitive element Cfstores (integrates) a signal current from a photoelectric conversionelement 101 through a TFT 102 and is connected between the invertingterminal and an output terminal Vout of the operational amplifier. Aswitch SW-H is connected in parallel to the capacitive element Cf toreset the integrated signal charges or refresh the photoelectricconversion element 101 through the TFT 102. The switch SW-H iscontrolled by an RC signal.

A power supply Vg(on) turns on the TFT 102 to transfer signal charges tothe capacitive element Cf. A power supply Vg(off) turns off the TFT 102.A switch SW-D switches between the power supply Vg(on) and the powersupply Vg(off).

To refresh the photoelectric conversion element 101, the switch SW-Gmust be set on the reset bias V(reset) side to turn on a switch SW-E.Simultaneously, the switch SW-D must be set on the power supply Vg(on)side.

FIG. 13 is a timing chart showing the circuit operation of one pixel ofthe X-ray imaging apparatus shown in FIG. 12.

The circuit operation of one pixel having the photoelectric conversionelement 101 and TFT 102 will be described with reference to FIGS. 12 and13.

The operation during the X-ray irradiation period is the same as in theabove-described first embodiment, and a description thereof will beomitted. During the X-ray irradiation period, the switch SW-D is set onthe V(off) side, the switch SW-G is set on the V(reset) side, and theswitch SW-H is turned off.

A transfer period will be described next.

In the transfer operation, the switch SW-D is set on the Vg(on) side toturn on the TFT 102. With this operation, electron carriers (Se)corresponding to the number (Sh) of hole carriers stored upon X-rayirradiation flow from a C₂ side to the G electrode side through the TFT102. Accordingly, the charges are stored in a capacitive element Cf. Thepotential on the output terminal side of the operational amplifierchanges (drops) by an amount equal to the signal amount. At this time,Se and Sh hold Se=Sh×C_(SiN)/(C_(SiN)+C_(i)). The potential of the readcapacitor C₂ is virtually grounded by the bias V(reset) at thenoninverting terminal (+) of the operational amplifier and thereforedoes not change.

A refresh operation will be described next.

The timing chart of FIG. 13 shows the potentials of the D electrode, Gelectrode, and node N when Vs=9 (V), Vg(reset)=2 (V), and V(refresh)=6(V) and the capacitance component C_(i) equals the capacitance componentC_(SiN) in the equivalent circuit diagram shown in FIG. 12.

In the refresh operation, the switch SW-H is turned on by the RC signal.The switch SW-D is set on the Vg(on) side. The switch SW-G is set on theV(refresh) side. With this operation, the potential of the G electrodeof the photoelectric conversion element 101 rises from the potential(V(reset)=2 (V)) at signal transfer to the refresh bias V(refresh)=6 V.Simultaneously, the potential of the node N also rises but does notexceed Vs=9 V. When the potential of the node N increases, some of thesignal charges (hole carriers) stored in the node N are discharged tothe D electrode side, so the refresh operation of the photoelectricconversion element 101 is executed.

A reset operation will be described next.

In the reset operation, the switch SW-D is kept on the Vg(on) side, andthe switch SW-H is kept ON. In this state, the switch SW-G is changedfrom the V(refresh) side to the V(reset) side. With this operation, theG electrode of the photoelectric conversion element 101 is reset to thereset bias V(reset). Simultaneously, the capacitive element Cf connectedto the output terminal of the operational amplifier is reset to thereset bias V(reset). That is, in the reset operation in which thepotential difference between the two terminals of the capacitive elementCf becomes zero, the potential of the node N attenuates from thepotential (9 V in FIG. 13) in the refresh operation. The attenuationamount ΔVN is ½ of the potential difference between V(refresh) andV(reset) when the capacitance component C_(i) equals the capacitancecomponent C_(SiN). In this description, the decrease amount is 2 V. Inaddition, the attenuation amount ΔVN of the node N decides the amount ofhole carriers stored in the next photoelectric conversion operation.

In FIG. 28 that shows the prior art, the wait period is prepared.However, no wait period is prepared in the timing chart shown in FIG.13. The reason will be described below with reference to FIGS. 14 and15.

FIG. 14 is an equivalent circuit diagram of the X-ray imaging apparatusaccording to the third embodiment. For the descriptive convenience, FIG.14 illustrates only 3×3=9 pixels which are two-dimensionally arrayed ina photoelectric conversion circuit section 10.

A read circuit section 21 reads the parallel signal outputs from thephotoelectric conversion circuit section 10, converts the outputs intoserial signals, and outputs them. Reference symbols A1 to A3 denoteoperational amplifiers connected to signal interconnections M1 to M3 andinverting terminals (−). Capacitive elements Cf1 to Cf3 are connectedbetween the inverting terminals (−) and the output terminals. Thecapacitive elements Cf1 to Cf3 integrate the currents based on theoutput signals from the photoelectric conversion elements 101 when theTFTs 102 are turned on and convert the currents into voltage amounts.Switches RES41 to RES43 reset the capacitive elements Cf1 to Cf3 to thereset bias V(reset). The switches RES41 to RES43 are connected inparallel to the capacitive elements Cf1 to Cf3.

A switch SW-res resets the noninverting terminals of the operationalamplifiers A1 to A3 to the reset bias V(reset) (0 V in FIG. 14). Aswitch SW-ref refreshes the noninverting terminals of the operationalamplifiers A1 to A3 to the refresh bias V(refresh). These switches arecontrolled by a “REFRESH” signal. When the “REFRESH” signal is “Hi”, theswitch SW-ref is turned on. When the “REFRESH” signal is “Lo”, theswitch SW-res is turned on. These switches are not simultaneously turnedon.

FIG. 15 is a timing chart showing the operation of the X-ray imagingapparatus shown in FIG. 14. FIG. 15 shows the operation of two frames.The operation of the photoelectric conversion device shown in FIG. 14will be described with reference to this timing chart.

A photoelectric conversion period will be described first.

The D electrodes of all photoelectric conversion elements S1-1 to S3-3are biased to a read power supply Vs (positive potential). All signalsin a shift register SR1 are “Lo”. All TFTs (T1-1 to T3-3) for switchingare OFF. When the light source is turned on in this state to emit apulse, the D electrodes (N+ electrodes) of the photoelectric conversionelements S1-1 to S3-3 are irradiated with light. Electron and holecarriers are generated in the i-layers of the photoelectric conversionelements S1-1 to S3-3. The electrons are moved to the D electrodes bythe read power supply Vs. Holes are stored in the interface between thei-layer and the insulating layer of each of the photoelectric conversionelements S1-1 to S3-3. The holes are held even after the X-rays areturned off.

A read period will be described next.

A read operation is performed in the order of the photoelectricconversion elements S1-1 to S1-3 of the first row, the photoelectricconversion elements S2-1 to S2-3 of the second row, and thephotoelectric conversion elements S3-1 to S3-3 of the third row.

First, to read the photoelectric conversion elements S1-1 to S1-3 of thefirst row, a gate pulse is applied from the shift register SR1 to a gateinterconnection G1 of the switch elements (TFTs) T1-1 to T1-3. At thistime, the high level of the gate pulse equals the externally suppliedvoltage Vg(on). Accordingly, the TFTs (T1-1 to T1-3) are turned on.Signal charges stored in the photoelectric conversion elements S1-1 toS1-3 flow as currents through the TFTs (T1-1 to T1-3). The currents flowinto the capacitive elements Cf1 to Cf3 connected to the operationalamplifiers A1 to A3 and are integrated.

Although not particularly illustrated in FIG. 14, a read capacitor isadded to each of the signal interconnections M1 to M3. The signalcharges are transferred to the read capacitors through the TFTs (T1-1 toT1-3). However, the signal interconnections M1 to M3 are virtuallygrounded by the reset bias (GND) at the noninverting terminals of theoperational amplifiers A1 to A3. Hence, the potentials are not changedby the transfer operation and held at GND. That is, the above-describedsignal charges are transferred to the capacitive elements Cf1 to Cf3.

The output terminals of the operational amplifiers A1 to A3 change asshown in FIG. 4 in accordance with the signal amounts of thephotoelectric conversion elements S1-1 to S1-3. Since the TFTs (T1-1 toT3-1) are simultaneously turned on, the outputs from the operationalamplifiers A1 to A3 simultaneously change. That is, parallel outputs areobtained. In this state, the “SMPL” signal is turned on. The outputsignals from the operational amplifiers A1 to A3 are transferred tosample-and-hold capacitors CL1 to CL3. When the “SMPL” signal is turnedoff, the signals are temporarily held.

When a pulse is applied from the shift register SR2 to switches Sr1,Sr2, and Sr3 in this order, the signals held by the sample-and-holdcapacitors CL1 to CL3 are output from a buffer amplifier Ab in the orderof the sample-and-hold capacitors CL1, CL2, and CL3. As a result,photoelectric conversion signals of one row including the photoelectricconversion elements S1-1, S1-2, and S1-3 are sequentially converted intoserial signals and output. The read operation of the photoelectricconversion elements S2-1 to S2-3 of the second row and the readoperation of the photoelectric conversion elements S3-1 to S3-3 of thethird row are executed in the same way as described above.

When the signals of the operational amplifiers A1 to A3 are sampled andheld by the sample-and-hold capacitors CL1 to CL3 in accordance with theSMPL signal of the first row, the signals of the photoelectricconversion elements S1-1 to S1-3 are output from the photoelectricconversion circuit section 10. Hence, the refresh operation of thephotoelectric conversion elements S1-1 to S1-3 in the photoelectricconversion circuit section 10 and the reset operation of the capacitiveelements Cf1 to Cf3 can be executed while the signals are being seriallyconverted by the switches Sr1 to Sr3 in the read circuit section 21.

The refresh operation of the photoelectric conversion elements S1-1 toS1-3 is attained by changing the “REFRESH” signal to “Hi” to turn on theswitch SW-ref, turning on the switches RES41 to RES43 by the “RC”signal, and applying the voltage Vg(on) to the gate interconnections ofthe TFTs (T1-1 to T3-1). That is, the G electrodes of the photoelectricconversion elements S1-1 to S1-3 are refreshed to the refresh biasV(refresh). Then, the reset operation starts.

Subsequently, in the reset operation, while the voltage Vg(on) isapplied to the gate interconnections of the TFTs (T1-1 to T3-1), and theswitches RES41 to RES43 are kept ON, the “REFRESH” signal is set to“Lo”. With this operation, the G electrodes of the photoelectricconversion elements S1-1 to S1-3 are reset to the reset biasV(reset)=GND. Simultaneously, the signals stored in the capacitiveelements Cf1 to Cf3 are reset.

After the end of the reset operation, a gate pulse can be applied to thegate interconnection G2. More specifically, the signals of the first roware serially converted by the shift register SR2. During this time, thephotoelectric conversion elements S1-1 to S1-3 are simultaneouslyrefreshed, the capacitive elements Cf1 to Cf3 are reset, and the signalcharges of the photoelectric conversion elements S2-1 to S2-3 of thesecond row can be transferred to the signal interconnections M1 to M3through the shift register SR1. With the above operation, the signalcharges of all the photoelectric conversion elements S1-1 to S3-3 of thefirst to third rows can be output.

When the above-described photoelectric conversion period and read periodare repeated, continuous moving images can be acquired.

The timing chart of this embodiment is different from the timing chartof the prior art shown in FIG. 30 in that the refresh period is notpresent in this embodiment. When the refresh period is omitted, theframe frequency in acquiring moving images can accordingly be increased.In the prior art, all the photoelectric conversion elements arerefreshed at once. Hence, the wait period to relax the variation in GNDor power supply due to the dark current component in the refresh modemust be prepared. In this embodiment, however, the photoelectricconversion elements are refreshed for each row. Since the number ofphotoelectric conversion elements to be refreshed at once is muchsmaller than in the prior art, no particular wait period is necessary.Accordingly, the frame frequency can be increased.

In the above-described X-ray imaging apparatus according to thisembodiment, the subject is irradiated with X-rays as pulses. However,X-ray irradiation may be done continuously (in a DC manner). This casewill be described below.

FIG. 16 is a timing chart showing an operation performed when the X-rayimaging apparatus according to the third embodiment is continuously (ina DC manner) irradiated with X-rays.

In this case, the photoelectric conversion period is a period after theend of refresh until the start of transfer. In an actual medical X-rayimaging apparatus, the photoelectric conversion circuit section isconstituted by a number of pixels of N rows×M columns. For example, forthe photoelectric conversion elements of the first row, the actualphotoelectric conversion period equals the read period of the (N−1) rowsfrom the second to Nth rows except the transfer, refresh, and resetperiods of the photoelectric conversion elements. This also applies tothe photoelectric conversion elements of the remaining rows. For them,the actual photoelectric conversion period equals the read period of the(N−1) rows except the transfer, refresh, and reset periods of thephotoelectric conversion elements.

For example, for the photoelectric conversion elements of the 100th row,the actual photoelectric conversion period equals the sum of the readperiod from the 101st to Nth rows and the read period from the first to99th rows in the next frame, i.e., the read period of the (N−1) rows.That is, if a subject is irradiated with X-rays in a DC manner, thephotoelectric conversion period extends over two frames. However, sincethe photoelectric conversion period is the same, no special problem isposed.

When a subject is continuously (in a DC manner) irradiated with X-rays,the X-ray irradiation period shown in FIG. 2 or the photoelectricconversion period shown in FIG. 4 can be omitted. For this reason, theframe rate of moving images can be further increased. In addition, ascompared to the pulse irradiation method, the intensity of X-rays can bereduced. Hence, the load on the tube serving as the X-ray source can bedecreased. Furthermore, since the X-ray high-voltage power supply neednot be pulse-controlled, the load on the X-ray power supply can bereduced.

(Fourth Embodiment)

FIG. 17 is an equivalent circuit diagram of one pixel of an X-rayimaging apparatus according to the fourth embodiment of the presentinvention. In the equivalent circuit diagram of the third embodimentshown in FIG. 12, the D electrode of the photoelectric conversionelement 101 is biased by the predetermined voltage Vs. In the fourthembodiment, however, a voltage Vs and voltage Vref can be switched by aswitch SW-F.

As a characteristic feature of this embodiment, the voltage from the Gelectrode side or that from the D electrode side can be selected as anapplication voltage to execute the refresh operation of a photoelectricconversion element 101. For example, to acquire one still image, arefresh bias is applied from the D electrode side. That is, an operationbased on the timing chart shown in FIG. 28 is executed. On the otherhand, to acquire a plurality of still images, a refresh bias is appliedfrom the G electrode side. That is, an operation based on the timingchart shown in FIG. 13 or 16 is executed. In this embodiment, both theconventional mode for obtaining a still image (imaging mode or stillimage mode) and the mode for acquiring a moving image (fluoroscopy modeor moving image mode) can be executed by a single X-ray imagingapparatus.

FIG. 18 is an equivalent circuit diagram of the X-ray imaging apparatusaccording to the fourth embodiment.

The equivalent circuit diagram shown in FIG. 18 is different from. FIG.14 in that the bias line of the sensor can be switched between thevoltage Vs and the voltage Vref by a control signal VSC.

FIG. 19 is a timing chart showing an operation performed when thefluoroscopy mode (moving image mode) of the X-ray imaging apparatusaccording to the fourth embodiment is changed to the imaging mode (stillimage mode) to execute imaging.

FIG. 20 is a timing chart showing the operation in the fluoroscopy modeof the X-ray imaging apparatus shown in FIG. 18. That is, in thefluoroscopy mode, the timing operation shown in FIG. 19 is repeated.During this period, the radiographer monitors the fluoroscopic image ofthe object (patient) to decide the position or angle of the patient inobtaining a still image. Generally, the intensity of X-ray irradiationduring this period is relatively low. When the radiographer inputs anirradiation request signal (a decision signal for obtaining a stillimage) to the apparatus, the fluoroscopy mode changes to the imagingmode. FIG. 22 shows the operation timing in the imaging mode. In theflow of the fluoroscopy mode and imaging mode, the number of times ofimaging mode is not limited to one, as shown in FIG. 19. The modes maybe repeated as fluoroscopy mode→ imaging mode→ fluoroscopy mode→ imagingmode . . . in accordance with the imaging composition of the object.

FIG. 21 is another timing chart in the fluoroscopy mode shown in FIG.19, which is different from FIG. 20. The difference from FIG. 20 is thatthe subject is not irradiated with X-rays as pulses. Since the read andphotoelectric conversion can be executed in the same period, theoperation frequency in the fluoroscopy mode can be increased. Inaddition, since no X-rays as pulses are used, the load on the X-raygeneration source can be reduced.

When the X-ray imaging apparatus of the present invention is applied toa fluoroscopic apparatus, continuous images are acquired in thefluoroscopy mode while executing refresh from the switch side of a readcircuit section 21 through TFTs. When positioning is ended byfluoroscopy, and the fluoroscopy mode is changed to the still imagemode, refresh can be executed from the switch SW-F to obtain a stillimage having a high S/N ratio. That is, generally, the efficiency ishigher and the S/N ratio is also higher in refresh from the switch SW-Fside than in refresh from the TFT side. It is reasonable that inobtaining a fluoroscopic positioning image that allows a relatively lowS/N ratio, refresh from the side of the switch of the read circuitsection 21 is employed. On the other hand, in obtaining a still imagethat requires a high S/N ratio and high image quality, refresh from theswitch SW-F side is employed.

(Fifth Embodiment)

FIG. 23 is a schematic view showing an application example of theradiographic apparatus according to the present invention to an X-raydiagnostic system.

X-rays 6060 generated by an X-ray tube 6050 are transmitted through abreast part 6062 of a patient or examination subject 6061 and becomeincident on a radiographic apparatus (image sensor) 6040. The incidentX-rays contain the internal information of the examination subject 6061.In accordance with the incidence to the X-rays, they are converted intovisible light. The visible light is photoelectrically converted toobtain an electrical signal. This electrical signal is converted into adigital signal, subjected to image processing by an image processor6070, and observed on a display 6080 in a control room.

The image information can be transferred to a remote site through atransmission device such as a telephone line 6090 and displayed on adisplay 6081 or stored in a storage device such as an optical disk atanother site such as a doctor room so that a doctor who is at the remotesite can also diagnose the image. The image information can also berecorded on a film 6110 by using a film processor 6100.

An X-ray imaging system has been described in the above embodiments.However, the present invention can also be applied to an apparatus whichconverts radiation such as α-, β-, or γ-rays into light andphotoelectrically converts the light.

The photoelectric conversion element array of the present invention canalso be used in a normal imaging apparatus for detecting visible lightor infrared light. As a switching element that can be used in thepresent invention, a thin film transistor whose channel region is formedby using an amorphous semiconductor such as hydrogenated amorphoussilicon is preferably used. The form of the transistor is not limited toa lower gate stagger type. An upper gate stagger or upper gate coplanartype may also be used.

According to the radiographic apparatus according to each of the aboveembodiments, the conversion elements are sequentially refreshed for eachrow. Since the frame frequency in acquiring moving images can beincreased, the moving images can be obtained at a high speed. Inaddition, as compared to a case wherein all the conversion elements arerefreshed at once, the dark current (transient current) in the refreshmode can be made small. Hence, the voltage variation in GND or powersupply line can be suppressed. Also, the wait time necessary forrelaxing the voltage variation can be omitted.

As another characteristic feature of the above embodiments, since theconversion elements and switch elements are made of an amorphous siliconsemiconductor, the conversion elements and switch elements can be formedon the same substrate in the same step by a very simple process. Forthis reason, a very inexpensive X-ray imaging apparatus can be providedat a high yield. In addition, an obtained moving image can be extractedas an electrical signal by photoelectrical conversion and therefore caneasily be converted into digital data. When the digital information is,e.g., recorded or displayed for diagnosis of a person or object to beexamined, the diagnosis can be very efficiently executed in terms oftime and cost as compared to analog information. Hence, a more advancedmedical environment than now can be established in the future aging andIT society.

As many apparently widely different embodiments of the present inventioncan be made without departing from the spirit and scope thereof, it isto be understood that the invention is not limited to the specificembodiments thereof except as defined in the appended claims.

1. An imaging apparatus comprising: a plurality of pixels arrayed in arow direction and in a column direction, and each including a conversionelement that converts incident light into an electrical signal and aswitch element that is connected to the conversion element and transfersthe electrical signal; a plurality of control interconnections eachconnected to each of the plurality of switch elements arrayed in the rowdirection; a plurality of signal interconnections each connected to eachof the plurality of switch elements arrayed in the column direction; arefresh device which is connected to said plurality of signalinterconnections and applies a first bias to said plurality of signalinterconnections for refreshing the conversion elements of each row; anda reset device which is connected to said plurality of signalinterconnections and applies a second bias to said plurality of signalinterconnections for resetting said plurality of signalinterconnections.
 2. The apparatus according to claim 1, furthercomprising: a driving circuit section which is connected to theplurality of control interconnections, and supplies driving signals tothe plurality of control interconnections; and a read circuit sectionwhich is connected to the plurality of signal interconnections forreading out the electrical signals from the plurality of conversionelements row by row, said read circuit section including said refreshdevice and said reset device.
 3. The apparatus according to claim 2,wherein said read circuit section further includes an amplifier thatamplifies the electrical signal read out to the signal interconnection,a storage device which temporarily stores the amplified electricalsignal, and a serial conversion device which serially converts thestored electrical signal.
 4. The apparatus according to claim 2,wherein, after the read is executed, said read circuit section turns onthe switch element, and drives said refresh device to refresh theconversion elements row by row, and then, drives the reset device toreset the signal interconnection.
 5. The apparatus according to claim 1,wherein the conversion element and the switch element contain amorphoussilicon.
 6. The apparatus according to claim 1, wherein the conversionelement and the switch element are formed on the same substrate in thesame step.
 7. The apparatus according to claim 1, wherein saidconversion element comprises a first metal thin-film layer that isformed on a substrate as a lower electrode, an insulating layer that isformed on said first metal thin-film layer and made of amorphous siliconnitride that inhibits passage of electrons and holes, a photoelectricconversion layer that is made of hydrogenated amorphous silicon andformed on said insulating layer, an n-type injection inhibiting layerthat is formed on said photoelectric conversion layer and inhibitsinjection of the holes, and a transparent conductive layer that isformed on said injection inhibiting layer as an upper electrode or asecond metal thin-film layer that is formed on part of said injectioninhibiting layer, said switch element is formed on the same substrate asthat of the conversion element and comprises a first metal thin-filmlayer that is formed on the substrate as a lower gate electrode, a gateinsulating layer that is formed on said first metal thin-film layer andmade of amorphous silicon nitride, a semiconductor layer that is made ofhydrogenated amorphous silicon and formed on said gate insulating layer,an n-type ohmic contact layer that is formed on said semiconductorlayer, and a transparent conductive layer or a second metal thin-filmlayer that is formed on said ohmic contact layer as a source/drainelectrode, in a refresh mode, an electric field is applied to theconversion element in a direction to guide the holes from saidphotoelectric conversion element to said second metal thin-film layer,in a photoelectric conversion mode, an electric field is applied to saidconversion element in a direction to make the holes generated by thelight that is incident on said photoelectric conversion layer stay insaid photoelectric conversion layer and guide the electrode to saidsecond metal thin-film layer, and the holes that are stored in saidphotoelectric conversion layer or the electrons that are guided to saidsecond metal thin-film layer in the photoelectric conversion mode aredetected as an optical signal.
 8. The apparatus according to claim 1,further comprising a bias interconnection which applies a bias to theconversion element.
 9. The apparatus according to claim 8, wherein saidconversion element has at least two electrodes comprising a firstelectrode connected to the switch element and a second electrodeconnected to said bias interconnection, in a moving image mode, saidread circuit section turns on the switch element and drives the refreshdevice to execute the refresh operation of the photoelectric conversionelement, and in a still image mode, the bias is switched by a secondswitch connected to said bias interconnection to execute the refreshoperation of the conversion element.
 10. A method of driving an imagingapparatus including a plurality of pixels arrayed in a row direction andin a column direction, and each including a conversion element thatconverts incident light into an electrical signal and a switch elementthat is connected to the conversion element and transfers the electricalsignal, and a plurality of signal interconnections each connected toeach of the plurality of switch elements arrayed in the columndirection, said method comprising the steps of: driving the switches ofa predetermined row and transferring electrical signals converted by theconversion elements of the predetermined row; driving the switches ofthe predetermined row and refreshing the conversion elements of thepredetermined row; driving the switches and resetting the plurality ofsignal interconnections; and driving the switches of a next row of thepredetermined row and transferring electrical signals converted by theconversion elements of the next row.
 11. The method according to claim10, wherein said imaging apparatus further includes a plurality ofcontrol interconnections each connected to each of the plurality ofswitch elements arrayed in the row direction, a driving circuit sectionwhich is connected to the plurality of control interconnections, andsupplies driving signals to the plurality of control interconnections,and a read circuit section which is connected to the plurality of signalinterconnections for reading out the electrical signals from theplurality of conversion elements row by row.
 12. The method according toclaim 10, wherein said imaging apparatus further includes a refreshdevice which is connected to said plurality of signal interconnectionsand applies a first bias to said plurality of signal interconnectionsfor refreshing the conversion elements of each row, and a reset devicewhich is connected to said plurality of signal interconnections andapplies a second bias to said plurality of signal interconnections forresetting said plurality of signal interconnections.